Results: A new carbon nanotube sensor developed at MIT is the first sensor that can reversibly detect nitric oxide, a gas that cells commonly use to communicate with each other. Because the nitric oxide-carbon nanotube binding is reversible, the sensor can be used multiple times.

Why it matters: Nitric oxide is notoriously difficult to detect because it is so unstable. Monitoring nitric oxide levels in living cells, in real time, could help researchers figure out its role in cancer and other diseases. It would also allow closer study of nitric-oxide-releasing cancer drugs now in clinical trials. Biologists could also use such sensors to study nitric oxide's effects on the brain, where it acts as a neurotransmitter. Michael Strano, associate professor of chemical engineering and leader of the research team, says the advance will enable scientists to begin to answer some fundamental, long-standing biological questions.

How they did it: The researchers coated carbon nanotubes with a polymer designed to specifically attract nitric oxide. The polymer is wrapped tightly enough that only small molecules can get through to bind the nanotube, and the nitric oxide is strongly attracted to the nanotube by an extra pair of electrons passed from the polymer to the nanotube. The sensor is activated by near-infrared light, which easily penetrates the human body (biological tissues are relatively transparent to this kind of light).

Next steps: The team plans to start testing the sensors in living animals, and is working on similar sensors that can detect molecules other than nitric oxide.